In the engineering field in which data identification is performed automatically, there is currently a prominent trend toward adoption of RFID systems, in which an RFID transponder (also called an RFID tag) is attached to an object as a means of identifying data relating to the object, and response signals from the RFID transponder are received.
One example of such an RFID system is the invention disclosed in Patent Document 1. The invention disclosed in Patent Document 1 has the characteristic of oversampling data signals to increase data decoding probabilities.
Here, as the format of signals sent from an RFID transponder to an RFID interrogator, for example in ISO 18000-6, after the 16-bit preamble interval, data bits follow, as shown in FIG. 1.
Further, as the pattern representing data, in ISO 18000-6 the pattern shown in FIG. 2 is stipulated. As shown in FIG. 2A, as the pattern for FM0 encoding, taking as reference a clock signal with 50% duty, as the “1” and “0” logic, for data logical “0” the first half is High level and the second half is Low level, or, the first half is Low level and the second half is High level. For data “1”, over 100% of the clock signal period the level is Low, or is at High level.
FIG. 2B is the case of an FM1 encoding pattern, in which the data logical “0” and “1” is the reverse of that for FM0 encoding.
As the method for decoding logical “0” or “1” from this FM0 (or FM1) encoding pattern, taking FM0 as an example, in a method of the prior art, after DC component for the FM0 is removed, and when the time duration from the rising edge to the falling edge or the time duration from the falling edge to the rising edge is longer than a reference time duration, then a data “1” is output, and if two continuous durations shorter than the reference time duration occur, then data is decoded as “0”.
[Patent Document 1] U.S. Pat. No. 6,501,807